1. Field of the Invention
The invention relates to a die-cast casting apparatus and a die-cast casting method.
2. Description of the Related Art
A die-cast casting method is generally available by which products are cast within a short period of time and in large amounts by supplying a melt under a pressure into a die. Appropriate die-cast casting apparatuses are used in the die-cast casting method. The die-cast casting apparatuses used in the die-cast casting method may be broadly classified into hot-chamber die-cast machines in which a pressurization chamber for injecting a melt is disposed in a melt holding furnace and cold-chamber die-cast machines in which a pressurization chamber for injecting a melt is not disposed in a melt holding furnace. Cold-chamber die-cast machines will be described below.
A die-cast casting machine includes a die in which a cavity is formed when a fixed mold and a movable mold are pressed together, a cylindrical sleeve that communicates with the cavity via a runner formed in the die, a ladle that supplies the melt into the sleeve (pressurization chamber), and a plunger that injects the melt supplied into the sleeve (pressurization chamber) into the cavity.
In die-cast casting, the following four steps are implemented in the stated order by using the above-described die-cast casting apparatus. First, the movable mold is pressed against the fixed mold and a cavity is formed in the die (mold clamping step); next, the melt is supplied into the sleeve with the ladle (melt pouring step); third, pressure is applied by the plunger to the space inside the sleeve, thereby injecting the melt supplied into the sleeve into the cavity (injection step), and finally, separating the movable mold from the fixed mold and removing the molded casting (mold opening step).
The ladle used in the melt pouring step is a container open at the top that includes a melt pouring spout provided so as to protrude outward. The ladle scoops up a predetermined amount of the melt from a holding furnace where the melt is stored. Then, the ladle is moved to a predetermined position and thereafter tilted at the melt pouring spout side. As a result, the melt is poured from the melt pouring spout towards the melt supply gate provided in the sleeve and the melt is supplied to the sleeve.
When the melt is thus poured into the melt supply gate of the sleeve by using the above-described ladle, the time period in which the entire melt is supplied from the ladle into the sleeve, that is, the pouring rate, is set by adjusting the speed at which the ladle is tilted (time required to tilt the ladle to a predetermined angle). When the pouring rate is low, that is, when a long time period is required to supply the melt from the ladle into the sleeve, the temperature of melt inside the sleeve decreases and the melt partially solidifies. Therefore, the resultant problem is not only that the casting time increases, but also that pressure propagation is reduced when the melt located in the sleeve is injected into the cavity by the plunger and casting pores (cavities) generated in the melt inside the sleeve cannot be completely eliminated. Accordingly, it is desirable to increase the pouring rate, that is, reduce the time period in which the melt is supplied from the ladle into the sleeve, but if the ladle tilting speed is too high, a large amount of melt is supplied into the pouring spout of the ladle. As a result, the melt can overflow from the pouring spout or be scattered and run over from the melt supply gate of the sleeve.
Accordingly, Japanese Patent Application Publication No. 2002-210551 (JP-A-2002-210551) describes a technique of configuring a melt pouring spout of a ladle as an almost cylindrical tube and providing a partition plate along the axial direction inside the pouring portion, thereby adjusting the flow of melt in the pouring portion of the ladle and preventing the melt from scattering and running over from the melt supply gate of the sleeve when the melt is poured.
However, with the technique described in JP-A-2002-210551, the melt and air cannot efficiently replace each other in the pouring portion of the ladle when the melt is poured and the pouring rate is insufficient.